Aflatoxin in Arizona Cottonseed: A Model Study of Insect-Vectored Entry of Cotton Bolls by Aspergillus flavus

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Abstract
Insects have been implicated in the aflatoxin problem of cotton, but model studies have not been conducted to study insect-vectored entry of the Aspergillus flavus into bolls. Carpel walls of green bolls 12, 19, 26, 33, and 40 days after flowering were punctured to simulate damage of sucking insects or drilled to simulate the hole caused by exit of pink bollworm larvae. A. flavus was dusted on wound sites. Treated bolls were harvested 4, 6, 10, and 30 days after injury-inoculation. Microscopic examination followed fungal progression from wound sites to seeds, and chemical assays on individual seeds determined the pattern of aflatoxin-contaminated seeds to uncontaminated seeds. Six days were required for fungal penetration to seed surfaces. Drying was necessary for fungal entry into seed. The pattern of toxin to nontoxin seeds in locks from bolls injured by drilling and inoculated 33 days after flowering most closely resembled that pattern found in locks from naturally contaminated bolls. Results indicate that insect-vectored A. flavus entry and subsequent toxin infection are primarily of green bolls close to maturity and reinforce existing knowledge that control of insects lowers aflatoxin potential.